WASHINGTON – The fallout from the Boston Marathon bombings is threatening passage of immigration legislation, as conservative Republicans said on Capitol Hill, talk radio, and Twitter that the alleged participation of ethnic Chechen brothers shows the need for slowing down or halting the bill.

Tempers flared in a Senate hearing room on Monday when Senator Chuck Schumer, a New York Democrat, asserted that unnamed people are trying to use the Boston tragedy as an “excuse” to stymie the bill, prompting his colleague at the dais, Senator Charles Grassley, the Iowa Republican, to respond angrily, “I never said that, I never said that!”

The outburst came after a parade of conservative commentators – many of whom have been bristling at the sight of one of their favorite Republicans, Marco Rubio of Florida, leading the call for immigration legislation – used the Boston bombing as evidence that Rubio should stand down.

Ann Coulter, who specializes in vocalizing conservative outrage, tweeted: “It’s too bad Suspect number one won’t be able to be legalized by Marco Rubio, now.” That suspect, Tamerlan Tsarnaev, died in a shoot-out early Friday. Coulter’s comments came after radio host Rush Limbaugh, in an on-air interview with Rubio, said he couldn’t see how the legislation helps Republicans.

The flare-ups demonstrated anew how immigration remains one of the most volatile issues facing Congress, with divisions within the Republican Party barely beneath the surface, ready to bubble over with any new event. Supporters of the legislation sought once again Monday to play down conflicts, while Rubio took the unusual step of putting up a website dedicating to debunking what he calls “myths” about the legislation.

The Boston bombing “certainly is a distraction and offers a foothold for people who don’t want this to pass,” said Ross Baker, a congressional scholar at Rutgers University who is monitoring the debate. “It would be very hard to argue to pass this thing immediately. The bombings give opponents a much more plausible reason to say, ‘Hold on, let’s wait until all the facts are known,’ which of course takes momentum out of the bill.”

The Republican Party has been through a series of internal debates about the legislation since the GOP’s failed 2012 nominee, Mitt Romney, lost the presidential election. Romney had said during the campaign that undocumented immigrants should self-deport, a comment widely viewed as costing him considerable Hispanic support.

A report by the Republican National Committee said the party must find a way “to embrace and champion comprehensive immigration reform.” That was followed by Republican efforts to support a compromise version of the bill, which in turn alarmed some in the party who viewed the legislation as tantamount to amnesty.

Under the latest version of the bill, most of the 11 million undocumented immigrants would be eligible to apply for a green card after 10 years and eventually could obtain citizenship after paying a fine, back taxes, learning English, and passing a criminal background check.

The bill would also nearly double the number of high-skilled visas and create a new visa program for low-skilled jobs. The Department of Homeland Security would also have to establish a tracking system to monitor those who overstay their visas.

Senator Rand Paul, the Kentucky Republican and a leader of the Tea Party movement, called on Monday for Congress to focus on strengthening national security before considering comprehensive immigration reform, noting that the Marathon bombings were allegedly done by immigrant brothers from Kyrgyzstan.

“The facts emerging in the Boston Marathon bombing have exposed a weakness in our current system. If we don’t use this debate as an opportunity to fix flaws in our current system, flaws made even more evident last week, then we will not be doing our jobs,” wrote Paul, in a letter to Senate majority leader Harry Reid.

Russian authorities in 2011 had flagged Tamerlan Tsarnaev as a follower of “radical Islam” and warned the FBI, which said it investigated the man but did not find evidence of terrorist activity.

Tamerlan, 26, had a green card but questions about his “moral character” were raised in the review of his application for citizenship. His younger brother, Dzhokhar Tsarnaev, 19, became a naturalized US citizen on Sept. 11, 2012.

The brothers are ethnic Chechens who immigrated to the United States about a decade ago from Kyrgyzstan, a former Soviet Republic in central Asia. Their aunt, Maret Tsarnaeva, has said she wrote the refugee petition in April 2002 for Dzhokhar and their parents to receive asylum in the United States. Tamerlan and his two sisters joined the family later.

Paul is the latest in a string of conservative Republicans seeking to use last week’s Boston terrorist attacks to delay comprehensive immigration reform.
The Senate Judiciary Committee continued debating the bipartisan immigration bill on Monday, its second hearing following the bill’s introduction last week. The committee is expected to continue vetting the bill through May, with the full Senate slated to begin debate in June.

Senator Patrick Leahy, a Vermont Democrat and chairman of the Senate Judiciary Committee, on Monday accused opponents of immigration reform of using the bombings as an excuse to thwart change.

“Last week opponents of comprehensive immigration reform began to exploit the Boston Marathon,” he said as he convened Monday’s hearings. “I urge restraint in that regard.”

Paul said no further changes should be made to immigration “until we understand the specific failures of our immigration system” and possibly an intelligence failure given that Tamerlan Tsarnaev had already been flagged by the FBI.

In his letter, Paul suggested temporarily suspending student visas from high-risk countries and called for heightened scrutiny before accepting refugees from such countries.

“The Senate needs a thorough examination of the facts in Massachusetts to see if legislation is necessary to prevent a similar situation in the future,” Paul said. “National security protections must be rolled into comprehensive immigration reform to make sure the federal government does everything it can to prevent immigrants with malicious intent from using our immigration system to gain entry into the United States in order to commit future acts of terror.”

During a Senate hearing on immigration last Friday, Grassley recommended that the Senate not rush to pass immigration reform before determining how people such as the Tsarnaev brothers “who wish to do us harm” will not stand a chance to benefit.

But House Speaker John A. Boehner, in a sign of solidarity with Rubio and other Republicans who support the bill, said on Fox News that “if we fix our immigration system it may actually help us understand who all is here, why they’re here, and what legal status they have.”

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